Rubber compositions containing high levels of plasticizer are known. For example, U.S. Pat. No. 4,429,068 to Nakahira discloses a cured rubber having specific physical properties obtained by curing a rubber composition comprising 100 parts by weight of a rubber component, 5 to 2,000 parts of a factice, and 20 to 2,000 parts of a softening agent. The reference states that the rubber composition can be used in golf ball cores.
U.S. Pat. No. 5,776,294 to Nagel discloses a method of providing curable elastomers crosslinked with the aid of metal salts of a, β-ethylenically unsaturated carboxylic acids and, optionally an alkyl aminoalkyl phenol vulcanization inhibitor. Examples are given of metal salts of acrylic and methacrylic acids mixed with ethylene propylene diene rubber and high levels of Sunpar 2280, a proprietary plasticizer available from Sun Refining and Marketing Company, Philadelphia, Pa.
U.S. Pat. No. 6,380,291 to von Hellens discloses rubber compositions comprising an acrylate or methacrylate salt, an elastomer curable with a peroxide initiator, and a plasticizer having one or more epoxide groups per molecule. The reference states that the plasticizer should be present in the rubber composition in an amount of from about 2 to about 20 phr. The reference also states that golf balls are a typical end use.
In the golf ball industry, rubber compositions containing high levels of plasticizer are known to be useful as the inner core layer material in thread wound golf balls. For example, U.S. Pat. Nos. 6,593,443 and 6,669,581 to Iwami and U.S. Pat. No. 6,846,247 to Kato disclose a wound golf ball, wherein the inner core layer is preferably obtained by vulcanizing and molding a rubber composition containing an oily substance, such as a petroleum compounding oil, a plasticizer, a rubber substitute (factice), alkylbenzene, and liquid rubber. The references state that the oily substance is preferably contained in the base rubber in an amount of about 30 to 500 parts, based on 100 parts of the base rubber.
A desire remains for novel rubber compositions containing high levels of an oily substance, which are useful in solid golf ball applications. Such compositions may provide one or more of the following properties relative to previously known golf ball materials: low cost, ease of processing, reduced compression, and reduced velocity. The present invention describes such compositions and their use in a variety of golf ball core, cover, and intermediate layers.